The present invention relates to polymeric coatings for developer, or xe2x80x9cdonorxe2x80x9d members used in electrophotographic image development systems. In xerography, or electrophotographic printing, a charge retentive surface called a photoreceptor is electrostatically charged, then exposed to a light pattern of an original image to selectively discharge the surface in accordance with the image, i.e., xe2x80x9cimagewisexe2x80x9d. The resulting pattern of charged and discharged areas on the photoreceptor form an electrostatic charge pattern (xe2x80x9clatent imagexe2x80x9d) conforming to the original. The latent image is developed by contacting it with a finely divided electrostatically attractable powder called xe2x80x9ctoner.xe2x80x9d Toner is held on the image areas by the electrostatic charge on the photoreceptor surface. Thus, a toner image is produced in conformity with a light image of the original being reproduced. The toner image may then be transferred to a substrate or support member such as paper, and the image is affixed to the paper to form a the desired permanent image on the substrate. After development, excess toner left on the charge retentive surface is cleaned from the surface.
The step of conveying toner to the latent image on the photoreceptor is known as xe2x80x9cdevelopment.xe2x80x9d The object of effective development of a latent image on the photoreceptor is to convey toner particles to the latent image at a controlled rate so that the toner particles effectively adhere electrostatically to the appropriately-charged areas on the latent image.
A commonly used development technique involves a single-component developer material. In a typical single-component development system, each toner particle has both magnetic properties, to allow the particles to be magnetically conveyed to the photoreceptor, and an electrostatic charge, to enable the particles to adhere to the photoreceptor. In such a system, the developer, or xe2x80x9cdonorxe2x80x9d member is a cylindrical sleeve (xe2x80x9cdonor rollxe2x80x9d) which rotates about a stationary magnet assembly. The magnetized toner particles adhere to the rotating sleeve by the force of the stationary magnets within the sleeve. As the sleeve rotates around the magnets, particles adhering to the sleeve are exposed to an alternating series of magnetic polarities. The developer roll has a conductive coating which facilitates the adherence of toner to its surface. The coating typically includes a conductive pigment and a binder composition.
The option of eliminating organic solvents from coating procedures has many benefits. It eliminates the need to build a coating plant to the stringent and costly Class I Division I or II (xe2x80x9cexplosion proofxe2x80x9d) specification for the use of flammable liquids. Since engineering controls, such as classified rooms and fume hoods, can only reduce the risk, there is a health and safety benefit to the plant operators in replacing organic solvents with water. The need to reclaim, destroy or account for the volatile organic compound (VOC) emissions is removed, which also provides cost savings. Also, by reducing or even eliminating VOC emissions, the plant design can be consistent in many locations, despite any variations in local regulations.
The present invention relates to improved donor members having coatings thereupon which are made via an environmentally friendly process and without the drawbacks of prior attempts at water-based donor member coatings. Before the present invention, grinding of pigment into water-based phenolic resins, unlike organic-based coatings, was very likely to result in dispersion thickening and foaming. In extreme cases this foam is very stiff (meringue-like) and unsuitable for coating. Even small amounts of air entrainment can result in coating defects.
The present invention relates to improved methods of coating donor members with waterbome coatings, wherein a resin, a pigment, and water are combined in proportions effective to provide a donor member precursor composition; the donor member precursor composition is subjected to high pressure communition to provide a donor member conductive coating composition; and the donor member coating composition is coated onto a substrate. The present method advantageously provides a donor member coating which is substantially free of air pockets or other defects. The resin may be a phenolic resin, preferably a waterbome phenolic resin, such as Durez 33304 (Oxychem Chemical Corporation) or BB 317 (Neste Chemical), and in other preferred embodiments the pigment may be, e.g., carbon black, graphite, magnetite, nigrosine, or a combination of these pigments.
The high pressure communition step may be carried out using a high pressure communition device such as a piston homogenizer. One or two stage homogenizers may be used.
In another embodiment, the invention defines an image forming apparatus which has a charge-retentive surface to receive an electrostatic latent image, and a donor member for applying a developer material to develop the electrostatic latent image to form a developed image. The donor member is coated with a waterborne donor member coating composition prepared as described herein.
In yet another embodiment, the invention relates to coated donor rolls having a core with a coating composition thereupon, the donor member coating composition prepared by combining a resin, a pigment, and water in proportions effective to provide a donor member coating precursor composition; and subjecting the donor member coating precursor composition to high pressure communition.
Also included in this invention is an image forming apparatus including a charge-retentive surface for receiving an electrostatic latent image, and a donor roll having a core and a donor member coating prepared by a combining a resin, a conductive pigment, and water in proportions effective to provide a donor member conductive coating precursor composition, and subjecting the donor member conductive coating precursor composition to high pressure communition; and a transfuse component for transferring and fusing the developed image from the charge retentive surface to a copy substrate.
In another embodiment the invention encompasses an image forming apparatus having a charge-retentive surface for receiving an electrostatic latent image; and a donor roll to apply a developer material to the charge-retentive surface to develop the electrostatic latent image and form a developed image on the charge retentive surface. The donor roll is coated with a waterborne donor member coating composition of the invention. The image forming apparatus further includes a transfer component to transfer the developed image from the charge retentive surface to a copy substrate; and a fixing component to fuse the transferred developed image to the copy substrate.
In an even further embodiment, the invention includes an image forming apparatus for forming images on a recording medium, which has a charge-retentive surface for receiving an electrostatic latent image; and a donor roll with a core and a coating of the present invention for applying a developer material to the charge-retentive surface to develop the electrostatic latent image to form a developed image on the charge retentive surface. The apparatus also includes a transfuse component for transferring the developed image from the charge retentive surface to a copy substrate, and for fusing the developed image to the copy substrate.